The present invention relates to a thermal transfer recording medium improved in a hot-sticking resistance.
In a thermal transfer recording system, there is used a recording medium wherein a thermally transferable ink layer such as heat-meltable ink layer or heat-sublimatable ink layer is provided on one surface of a substrate. Print images are produced by bringing the thermally transferable ink layer of the recording medium in contact with a receiving medium such as plain paper while a thermal head is brought in contact with the back surface of the substrate of the recording medium, and selectively activating plural heating elements of the thermal head to heat localized areas of the thermally transferable ink layer, whereby the heat-meltable ink or sublimable dye in the heated areas of the ink layer is transferred onto the receiving medium.
Plastic films including polyethylene terephthalate film as a typical example are used as the substrate of the above-mentioned thermal transfer recording medium.
When a plastic film is used as the substrate, a portion of the plastic film which is in contact with the thermal head is adhered to the thermal head because the surface temperature of the thermal head exceeds the melting temperature of the plastic film during printing operation, whereby feeding of the recording medium is hindered. Such phenomenon is so-called "hot-sticking phenomenon".
In order to prevent such hot-sticking phenomenon, heretofore, a hot-sticking resistant layer composed of a heat resistant resin as a main component was provided on the surface of the plastic film which was brought in contact with the thermal head.
However, such conventional hot-sticking resistant layer has the following drawbacks due to the fact that the layer is a coating of a resin.
That is, in recent years, a high speed printing is also required for thermal transfer recording. The operation temperature of the thermal head must be set to a high temperature to increase the printing speed. However, it is not impossible to adopt a considerably high operation temperature for the thermal head since there is a limit in heat resistance of the conventional hot-sticking resistant layer due to the fact that it is composed of organic substances.
Further, there is a lower limit in thickness of a resin coating to obtain a coating having a uniform thickness. For the reason, the heat conduction of the recording medium is detracted by providing the hot-sticking resistant layer, which causes a disadvantage that unevenness of print images is marked with increasing printing speed.
An object of the present invention is to provide a thermal transfer recording medium improved in hot-sticking resistance which facilitates a high speed printing.
This and other objects of the invention will become apparent from the description hereinafter.